1. Field of the Invention
The present invention relates generally to the field of cardiopulmonary resuscitation. In particular, the invention relates to devices and methods for ventilating a patient in association with cardiopulmonary resuscitation procedures.
Worldwide, sudden cardiac arrest is a major cause of death and is the result of a variety of circumstances, including heart disease and significant trauma. In the event of a cardiac arrest, several measures have been deemed to be essential in order to improve a patient's chance of survival. These measures must be taken as soon as possible to at least partially restore the patient's respiration and blood circulation. One common technique, developed approximately 30 years ago, is an external chest compression technique generally referred to as cardiopulmonary resuscitation (CPR). CPR techniques have remained largely unchanged over the past two decades.
With traditional CPR, pressure is applied to a patient's chest in order to increase intrathoracic pressure. An increase in intrathoracic pressure induces blood movement from the region of the heart and lungs towards the peripheral arteries. Such pressure partially restores the patient's circulation. Traditional CPR is performed by actively compressing the chest by direct application of an external pressure to the chest. After active compression, the chest is allowed to expand by its natural elasticity which causes expansion of the patient's chest wall. This expansion allows some blood to enter the cardiac chambers of the heart. The procedure as described, however, is insufficient to ventilate the patient. Consequently, conventional CPR also requires periodic ventilation of the patient. This is commonly accomplished by mouth-to-mouth technique or by using positive-pressure devices, such as a self-inflating bag which relies on squeezing an elastic bag to deliver air via a mask, endotracheal tube or other artificial airway.
In order to increase cardiopulmonary circulation induced by chest compression, a technique referred to as active compression-decompression (ACD) has been developed. According to ACD techniques, the active compression phase of traditional CPR is enhanced by pressing an applicator body against the patient's chest to compress the chest. Such an applicator body is able to distribute and apply force substantially evenly over a portion of the patient's chest. More importantly, however, the applicator body is sealed against the patient's chest so that it may be lifted to actively expand the patient's chest during the decompression step. The resultant negative intrathoracic pressure induces venous blood to flow into the heart and lungs from the peripheral venous vasculature of the patient.
Other techniques for increasing cardiopulmonary circulation while performing CPR include impeding airflow into the patient's lungs during decompression of the patient's chest. Such techniques are described in U.S. Pat. Nos. 5,551,420 and 5,692,498, and in copending U.S. patent application Ser. No. 08/950,702. The complete disclosures of these references are herein incorporated by reference. In one particular embodiment, airflow into the patient's chest is impeded by placing a pressure-responsive valve in the patient's airway. The valve prevents the flow of air into the patient's lungs during the decompression phase until a threshold negative intrathoracic pressure is reached. At this point, the valve opens to allow airflow to the patient's lungs. Hence, when the valve is closed, the amount of negative intrathoracic pressure is increased, thereby enhancing the amount of venous blood flow to the heart and lungs.
When performing CPR, there is a need to periodically ventilate the patient. Some common techniques include mouth-to-mouth ventilation, ventilatory bags, and ventilation machines. However, as of yet there has been no effective and convenient way to coordinate the timing of ventilation with the chest compressions. For example, if mouth-to-mouth resuscitation is provided, the rescuer must count each chest compression, stop chest compressions when a predetermined number of chest compressions have been performed, manually ventilate the patient with the rescuer's mouth, and then return to performing chest compressions. Similar problems are experienced when using ventilatory bags. Moreover, with many manual ventilation techniques, it is difficult, if not impossible, to precisely control the timing and volume of air delivered to the patient.
Hence, it would be desirable to provide methods and devices for ventilating a patient in association with cardiopulmonary resuscitation procedures. It would be particularly desirable to provide a way to easily and conveniently coordinate the timing of chest compressions with ventilation. It would be further desirable to precisely control the volume of respiratory gases delivered to the patient.
2. Description of the Background Art
U.S. Pat. Nos. 5,551,420 and 5,692,498, previously incorporated by reference describe techniques for preventing airflow to the patient's lungs during the decompression phase of CPR.
ACD-CPR techniques are described in detail in Todd J. Cohen et al., Active Compression-Decompression Resuscitation: A Novel Method of Cardiopulmonary Resuscitation, American Heart Journal, Vol. 124, No. 5, pp. 1145-1150, November 1992; and Todd J. Cohen et al., Active Compression-Decompression: A New Method of Cardiopulmonary Resuscitation, The Journal of the American Medical Association, Vol. 267, No. 21, Jun. 3, 1992. These references are hereby incorporated by reference.
The use of a vacuum-type cup for actively compressing and decompressing a patient's chest during ACD-CPR is described in a brochure of AMBU International A/S, Copenhagen, Denmark, entitled Directions for Use of AMBU.RTM. CardioPump.TM., published in September 1992. The AMBU.RTM. CardioPump.TM. is also disclosed in European Patent Application No. 0 509 773 A1. These references are hereby incorporated by reference.